Upon transmitting a speech signal or an audio signal in, for example, a packet communication system or a mobile communication system, which is typified by Internet communication, compression techniques or coding techniques are often used to improve the efficiency of transmission of the speech signal or the audio signal. Recently, there is a growing need for techniques which simply encode a speech signal or an audio signal at a low bit rate and encode a speech signal or an audio signal of a wider band with high quality.
In order to meet this need, scalable coding techniques have been developed whereby it is possible to decode a speech signal or an audio signal from part of encoded information and it is possible to limit the degradation of sound quality even in a situation where packet loss occurs in speech signal or audio signal coding (see Non-Patent Literature 1). Non-Patent Literature 1, for example, discloses “EAVQ (Embedded Algebraic Vector Quantization),” a technique which divides spectrum data acquired by converting a predetermined time of an input signal into a plurality of sub-vectors and performs multi-rate coding on each sub-vector when a coding bit rate is 16 kbps to 24 kbps and when an input signal is determined to be a speech signal. Non-Patent Literature 2, Non-Patent Literature 3, and Patent Literature 1 also disclose a technique related to EAVQ disclosed in the above mentioned Non-Patent Literature 1.